In the second part of my two-part article about building the Daisy skiff (WoodenBoat Nos. 126 and 127), I included a sidebar showing how to modify a hand plane to include a guide rod for use when planing lapstrake plank bevels. This involved drilling and tapping a hole on each side of a smoothing plane’s body to receive a threaded rod in one or the other, depending on the direction of planing. The guide assures an accurate bevel in either traditional wood or glued-lap plywood construction. In our shop, this system has proved to be an unqualified success for the past 20 years of building lapstrake boats from 6′ to 26′ long.
However, I always had misgivings about advising someone to drill holes in what might be a fine heirloom plane meant to last generations. To a large extent, we are not owners of such tools but caretakers. Boring holes and tapping them for a guide bar might increase the value of a plane for a small number of boatbuilders, but it could harm its aesthetic value for most future woodworkers.
The magnetic guide presented here is an alternative that avoids that issue. It works just as well as the threaded-in rod to guide the planing of accurate, watertight plank bevels. It can be attached quickly to any steel- or iron-bodied plane without modifying the tool in any way, and it can be easily moved from one side to the other when reversing the direction of planing.
Harry BryanHere, a guide rod is being used in shaping the garboard bevel on a 10′ 6″-long, flat-bottomed Fiddlehead skiff. The rod rides along a 3⁄4″ round batten centered along the lined-off outboard edge of the second topside plank. The batten is nailed in place with 1″ wire brads set flush with the batten’s surface so the guide rod won’t catch on them. For this guide, I used stainless steel for the rod. The hardwood body, cherry in this case, is fitted with rare-earth magnets to hold it to the side of a No. 4 smoothing plane.
In the rod version, the hole is placed so that it holds the rod parallel to the sole and offset so that its lower edge will be 3⁄4″ higher. This offset corresponds to the thickness of a guide batten installed at the adjacent lined-off plank line, as shown in drawing A and the photo on the opposite page. Having the rod in contact with the batten while planing assures the accuracy of the plank bevel as it is being created.
Harry BryanThe guide rod’s bottom edge is parallel to the bottom of the plane and offset 3⁄4″ above it, matching the thickness of the batten nailed to the molds. A projection of the bevel being created, as shown in the dotted line, will always touch the mold at the point where the round batten is fastened.
The magnetized version shown here sets the proper rod height when the hardwood body is placed so that its lower edge is flush with the bottom of the plane sole, as shown in drawing A.
It might seem that a guide held only by magnets could shift in use without the builder’s notice, throwing off the accuracy of the bevel. This has not proven to be a problem. The rare-earth magnets specified here are strong, and setting washers under them, as shown in drawing B, increases their holding power. Also, the force on the rod when the tool is in use is relatively light, and it’s not enough to dislodge the magnets.
Harry BryanThe guide is made with a hardwood body and metal rod to the dimensions shown. I used stainless-steel for the rod. Its construction is straightforward but must be accurate, with holes bored on the drill press to ensure that they are perpendicular.
Drawing B gives the dimensions for the guide. The 1⁄4″-diameter rod, which is 6″ long, is pressed or lightly driven into a 15⁄64″ hole in the hardwood body. Despite its simplicity, the guide would be of little use if it were not accurately made, so use a drill press to ensure that all the holes are perpendicular to the surface.
A Forstner bit works best for the counterbores that receive the magnets and washers. The magnets should be set so that when they are screwed in place over their washers they are barely recessed below the face of the wood, which will prevent them from mar-ring the surface of the plane. If necessary, remove a few shavings of wood between the magnets so that the guide will seat firmly all the way to its ends, which will help to prevent the guide from moving in use.
As a lap bevel is planed, as shown in the photograph at left, the guide rod rides on a batten tacked to the molds at the lined-off plank marks representing the new plank’s outboard edge.
We have found that a 3⁄4″-thick batten works best for almost all boats, regardless of length. Such a batten will take a fair bend over widely spaced molds, yet there will be enough stiffness to resist movement due to the light pressure of the guide. Usually, a rectangular batten is used for this purpose.
Although such a batten can work well, it must be significantly twisted in the forward sections of most hulls in order to lie against the molds, which can complicate its fastening. We take the concept one step further: We use a 3⁄4″-diameter round batten, which requires no twist. By first accurately removing the batten’s corners on a table saw, not much work is needed with a hand plane and sandpaper to round it. The batten can then be fastened to the molds directly on the lined-off plank marks, using 1″ wire brads set flush with the batten’s surface so they will not interfere with the guide rod.
Source note: The rare-earth magnets used are 3⁄4″ outside diameter and 1⁄4″ thick. In the United States, they can be found at Magnet 4 Less as model No. NDO 45-3, or at K&J Magnetics Inc. part No. RC24DCS. In Canada, a source is Jobmaster Magnets Canada Inc., part No. NEO40NI.750DX.250CS8.